Hygiene, dental and general . ding to the law ofprobability and chance. To illustrate by an example from Mendels work: when apea plant which produces peas having a green color is crossedwith one producing peas of yellow color all the peas producedin the first generation are of a yellow color but if plants of thisfirst hybrid generation are crossed among themselves the peasproduced in the second generation are in a definite ratio ofthree yellows to one green. 80 HYGIENE OF REPRODUCTION 81 This law may be illustrated also from animal guinea pigs the crossing of a black strain with
Hygiene, dental and general . ding to the law ofprobability and chance. To illustrate by an example from Mendels work: when apea plant which produces peas having a green color is crossedwith one producing peas of yellow color all the peas producedin the first generation are of a yellow color but if plants of thisfirst hybrid generation are crossed among themselves the peasproduced in the second generation are in a definite ratio ofthree yellows to one green. 80 HYGIENE OF REPRODUCTION 81 This law may be illustrated also from animal guinea pigs the crossing of a black strain with a whitestrain produces in the first generation only black offspringbut if these pigs are bred among themselves the resulting off-spring are in the ratio of three black pigs to one white one. These results are most clearly understood in terms of thepresence and absence theory which assumes that the yellowpea and the black guinea pig possess factors in the germ cellfor yellow and black color, respectively, and that these color. Fig. 15.—Inheritance in guinea pigs showing where the color (black) dominatesover another color (white). (Kelicott.) factors are lacking in the green pea and the white pig. Sucha characteristic appears whenever it is present in one or bothof the germ cells united to create the new individual. Wehave here an explanation of the fact that offspring of thefirst generation all show a particular characteristic which hasbeen inherited from one of the parents. We call such a char-acteristic as blackness in the guinea pig a dominant character-istic and the white color a recessive characteristic. The fol-lowing diagram illustrating the inheritance in guinea pigsshows why the first generation is completely black. All ofthe ova produced by the female guinea pig contain the char-acteristic for blackness and although they are united withsperms which lack this characteristic for blackness they still 82 hygiene: dental and general carry the characteristic to the fertil
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecthygiene, bookyear1920
